Follow-up studies were conducted on the diffuse cutaneous leishmaniasis (DCL) from the Dominican Republic. Those with positive leishmanin skin tests in the endemic area generally exhibited lymphocyte proliferation to leishmanial antigen; in contrast to patients with DCL. Further observations on local heat treatment were made on one new DCL case and a previous drug-treated patient who relapsed. A number of leishmanial isolates from patients with known clinical features, known geographic origin and known virulence for the genetically susceptible BABL/c mouse are now available to correlate with results of biochemical taxonomy. The leishmanial isolates from the DCL cases are distinct from Western hemisphere species and appear to be a new group. ELISA and IHA serologic tests using antigens from cultured filariform larvae were developed for serodiagnosis of human strongyloides infection. Some of the findings on immune response in rats to experimental infections with S. ratti were applied to patients found infected with S. stercoralis. Lymphocyte proliferation to larval antigen was not found to be a useful or reliable criterion of infection. However, histamine release from IgE sensitized peripheral basophils after exposure to larval antigens was found to be a consistent indicator of human infection. Nature of the antigen causing histamine release is under study.